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There is observational evidence for inside-out growth of elliptical galaxiessince $z \gtrsim 2-3$, which is not driven by in-situ star formation. Manysystems at high redshift have small sizes $\sim 1kpc$ and surface brightnessprofiles with low Sersic indices n. The most likely descendants have, onaverage, grown by a factor of two in mass and a factor of four in size,indicating $r \propto M^{\alpha}$ with $\alpha \gtrsim 2$. They also havesurface brightness profiles with $n \gtrsim 5$. This evolution can bequalitatively explained on the basis of two assumptions: compact ellipticalspredominantly grow by collisionless minor or intermediate 'dry' mergers, andthey are embedded in massive dark matter halos. We draw these conclusions fromidealized collisionless mergers spheroidal galaxies - with and without darkmatter - with mass ratios of 1:1, 1:5, and 1:10. The sizes evolve as $r \proptoM^{\alpha}$ with $\alpha < 2$ for mass-ratios of 1:1. For minor mergers ofgalaxies embedded in dark matter halos, the sizes grow significantly faster andthe profile shapes change more rapidly. Mergers with moderate mass-ratios of1:5 give $\alpha \sim 2.3$ and a final Sersic index of $n = 9.5$ after doublingthe stellar mass. This is accompanied by a significant increase of the darkmatter fraction within the stellar half-mass radius, driven by the strong sizeincrease probing larger, dark matter dominated regions. Only a few intermediatemass-ratio mergers of galaxies embedded in massive dark matter halos can resultin the observed concurrent inside-out growth and the rapid evolution in profileshapes. Apart from negative stellar metallicity gradients such a 'minor' mergerscenario also predicts significantly lower dark matter fractions for $z \sim 2$compact quiescent galaxies and their rare present day analogues (abbreviated).

How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction?